Extinction coefficient, theoretical

The solvent used was 5 %v/v ethyl acetate in n-hexane at a flow rate of 0.5 ml/min. Each solute was dissolved in the mobile phase at a concentration appropriate to its extinction coefficient. Each determination was carried out in triplicate and, if any individual measurement differed by more than 3% from either or both replicates, then further replicate samples were injected. All peaks were symmetrical (i.e., the asymmetry ratio was less than 1.1). The efficiency of each solute peak was taken as four times the square of the ratio of the retention time in seconds to the peak width in seconds measured at 0.6065 of the peak height. The diffusivities obtained for 69 different solutes are included with other physical and chromatographic properties in table 1. The diffusivity values are included here as they can be useful in many theoretical studies and there is a dearth of such data available in the literature (particularly for the type of solutes and solvents commonly used in LC separations). 

The extinction coefficient for non-ahsorbing particles may be theoretically evaluated from the ligjit scattering theory developed by Mie (lU, 1 ). It is calculated from the relationship... 

A good absolute theoretical comparison of strength is represented by the area under the absorption bands in the visible spectrum, or less accurately by the molecular extinction coefficients at the maximum wavelength of absorption. 

Using the extinction coefficients given above, the example for p-carotene, a 1 % solution (1 g/100 ml or 10 mg/ml) would give a theoretical absorbance reading of 2592 AU. A 2 pg/ml solution should therefore give an absorbance reading of 0.518 AU however, as indicated earlier, the standard solution must be... 

Fig. 3. (a) Theoretically predicted extinction coefficients for materials having refractive indices, n, and size parameters, x, as predicted from Mie scattering theory and (b) the normalized extinction coefficient for a grain... 

The experimentally verified theoretical relationship for the extinction coefficient ae is given by... 

Owing to a low abundance in fullerene soot as well, and to a small near-UV extinction coefficient, it took until 1996 for the next higher fullerene, Cso, to be isolated and characterized by 13C NMR spectroscopy.64 The measured resonances were consistent with 20 groups of four symmetry-equivalent carbon atoms, and in combination with theoretical calculations on the structures and... 

Most of the theoretical papers dealing with the photodissociation of polyatomic molecules are included in Table 9 under specific headings. Lee et introduced the multidimensional reflection (MR) approximation to replace the quasi-diatomic model often used in the theoretical descriptions of polyatomic molecule photodissociation. They utilized the results of the MR approximation to examine the dependence of the extinction coefficient on i max— V, where is the frequency of maximum absorption, to obtain the slope and orientation of the co-ordinate of steepest descent on the upper state surface and to explain the dependence of the absorption cross-section from initially excited vibrational states on the orientation of this co-ordinate. 

Mitchell (41) treated theoretically the absorption of light by a mono-layer, showing that the apparent quantum efficiency could be directly proportional to the absolute temperature for certain condensed films. The molecular extinction coefficient cannot be deduced from that in solution it is, however, proportional to sin- d (where 6 is the angle... 

In this section we shall analyze the relationship between the electronic structures and the absorption intensities in details. The intensity of the electronic transition is experimentally obtained as an area of the absorption spectrum displ ed with the abscissa of the energy linear scale(for example cm , eV,etc.) and the ordinate of the molar extinction coefficients and the experimental value corresponds to the theoretically obtained oscillator strength of the electronic transition. The example is shown in Fig.3. ... 

In general, chemisorption will produce new spectral bands which are not characteristic of the adsorbate or the adsorbent. However, absence of such bands cannot be taken as evidence of an absence of chemisorption. A difficulty present in any attempt to make kinetic measurements is that extinction coefficients are often significantly altered as a result of adsorption. These changes, which cannot as yet be interpreted theoretically, make it difficult to correlate the observed absorbance with the coverage of adsorbed molecules. The change in extinction coefficient is dependent on both the adsorbate and the adsorbent. For example, an increase of e was observed with increasing coverage for ethylene adsorbed on copper oxide, whereas the reverse occurred with nickel oxide . ... 

Extinction coefficients obviously may be determined for suitable absorptions of species whose concentration is already known from non-spectroscopic investigations. The results obtained in this way are limited by the accuracy and availability of other methods for the estimation of the species in question. For many reaction intermediates, direct calculation of concentration is not possible, and until recently only theoretical estimates were available for the oscillator strengths of absorptions involving such species. 

Hug and Surbeck 35) have proposed the use of Ada. = daL — daR, the difference of the Raman differential scattering cross sections in left and right circularly polarized incident light. This is the Raman equivalent of the circular dichroism Ae = el — eR, where s is the decadic molar extinction coefficient and, unlike the measured (but not the theoretical) IR — IL which depends on both sample and instrumental factors, is solely a molecular parameter. They introduced a chirality number q defined by... 

Values of the constant, fotmd by selection, are quite possible. Light constants of the rate according to the value order agree with theoretical values of constants on the basis of quantum yields (O = 0,1 - 1) [167], being characteristic for radicals, and extinction coefficients (e - l(fl/m cm). Large value K4 = 1000 kg/mole for acetyl alkyl radicals may be caused by acetic acid, taking part in integration of free valency. It is known [168], that small quantities of low-molecular substance increase the rate of free valency travel by 3-7 orders in comparison with the rate of usual chemical reaction. 

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